1. Field of the Invention
The present invention relates to a radio-frequency module which wirelessly transmits and receives signals of different bands at the same time.
2. Description of the Related Art
As an example of recent communication methods for wirelessly transmitting and receiving signals of different bands at the same time, carrier aggregation is known. In a radio-frequency module supporting carrier aggregation, an antenna, a receive circuit, an amplifier circuit for amplifying a transmitting signal, and a separator are required for each band.
If the size of a radio-frequency module implementing carrier aggregation is reduced, isolation characteristics of each band are decreased. More specifically, if the size of a radio-frequency module is reduced, harmonic components of a transmitting signal amplified in a low-band amplifier circuit are more likely to leak into a high-band receive circuit.
Accordingly, in the radio-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2007-124202, a matching circuit included in a low-band amplifier circuit is not connected to a ground pattern within a substrate, but is connected to a ground terminal on the back surface of the substrate, so as to suppress a leakage of harmonic components of a transmitting signal into a high-band receive circuit via a ground pattern within the substrate.
However, the radio-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2007-124202 is effective in suppressing a leakage only via a ground pattern, and is not effective in suppressing a leakage via paths other than a ground pattern. This will be explained more specifically. In a radio-frequency module, electromagnetic coupling and electrostatic coupling (hereinafter simply referred to as “coupling”) may occur between devices or between transmission lines. If the size of the radio-frequency module is reduced, coupling is more likely to occur between the devices or between the transmission lines, and, due to this coupling, a path is more likely to be formed. In the radio-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2007-124202, it is not possible to suppress a leakage via a path formed by this coupling.